Beauty marks can certainly be beautiful. “But sometimes a mole can convert to something serious like melanoma,” says Rex Amonette, MD, vice president of the Skin Cancer Foundation. “Regular skin checks by a doctor are key to catching suspicious moles early.” These pictures will help you identify an unhealthy mark.

A harmless moleLooks like: A symmetrical mark uniform in color with smooth borders; its usually smaller than a quarter-inch.

Need to know: They crop up in early childhood. Study your spots once a month when you do a self-exam. Talk to your doctor if any change shape, color, or elevation, or bleed, itch, or crustpossible signs of skin cancer.

MelanomaLooks like: An asymmetrical mole with uneven borders that tend to be scalloped; its larger than a pencil eraser and may contain two or more shades of black, brown, red, white, or blue. It can be a new mole or one youve had.

Need to know: Melanoma is the most serious form of skin cancer since it can spread to other parts of the body. Caught early, its curable.

Actinic keratosisLooks like: Small crusty or scaly bumps or patches that can be tan, pink, red, or flesh-colored. They have a rough texture and may itch or feel tender to the touch.

Need to know: They are precancerous growths that usually develop on your face, lips, ears, scalp, neck, forearms, and backs of your hands. They dont always turn into cancer but should be removed.

Basal cell carcinomaLooks like: A reddish patch, pearly pink, red, or white bump, or sore that bleeds, oozes, or stays open for several weeks or heals and then comes back again.

Need to know: Unlike melanoma, basal cell carcinoma doesnt crop up in existing moles. Instead, it forms from skin damaged by sunburns and UV rays. If caught, its easy to treat and isnt life-threatening.

Squamous cell carcinomaLooks like: A thick, rough, wartlike growth, a scaly red patch with irregular borders, or an open sore that crusts or bleeds.

Need to know: They dont crop up in existing moles and are most common on the face, lower lip, neck, arms, scalp, backs of the hands, and ears in people with fair complexions. Typically squamous cell carcinoma can be cured if caught early.